If you're wondering why Apple is paying for Amazon credits, it's a long and fascinating story. But essentially, the complaint was that Apple Senior Vice President Eddy Cue strong-armed major publishers into a pricing agreement that ended up causing e-book prices to spike overnight.

The judgment was handed down in 2013, and Apple started sending iTunes credits to customers in 2014.

According to Amazon, here is how you apply those credits to a purchase:

Eligible customers do not need to do anything to receive these credits. If you are eligible, we have already calculated your credit for you and added it to your Amazon account. As long as you have credit remaining we will automatically apply it to your purchase of qualifying items through Amazon.com, an Amazon device or an Amazon app. The credit applied to your purchase will appear in your order summary as a gift card during checkout and in your account history. Eligible customers should have received a notification email from Amazon on June 21, 2016. This credit will expire at 11:59pm HST on June 24, 2017.